Hello everybody, been reading the forum for the past year - lots of helpful advice, thank you.
First time posting
My apologies for the length of this post.

I am building a UGJ system for my 20G tank.
I will skip the history and reasons why.

I have a Maxi-Jet 1200 pump (thinking of maybe using 2)
Decided on 3/8" pvc tubing (not pipe) due to height/tank size, also gives me greater flexibility for orientation.
Haven't decided on a hookup to the pump yet, probably 1/2" reduced to 3/8" (1/2" fits the pump output)

I was originally going to use 1/2" tubing on the whole system, however I thought it would be too large inner diameter, seeing as the whole system is about (16ft - 1/2", 22ft - 3/8") roughly, and wasn't sure about head pressure on the pump. (Hence me thinking about using 2 pumps)

My idea was to make 2 "spirals" of tubing and drill holes in various locations (to work more as a reverse ugf than a ugj)

I mainly want lots of upwards water movement through the gravel, not so much over the top of the gravel (4 species of shrimps aswell as bottom feeders in the tank)
I did not want to use ugf plates due to all the plants.

So I ask you very intelligent/experienced people, what are your thoughts on this system?
Mainly what size/how many holes should I be putting in the tubing (each "spiral" is roughly 10ft of tubing)
Also should I just do 2 seperate pumps/spirals, or hook up both pumps to a closed loop system with each pump fighting the other (don't like this idea much, although it might work?), or 1 pump on the closed loop system (again roughly 22ft of tubing length in this system, is the 1 pump strong enough?)

Any system that pumps tank water under the substrate, so it passes through the substrate back to the tank, is a under gravel filter. Your reasons for using it don't change what it does. The goal should be to get roughly equal flow from every hole in the tubing. That requires that the total area of the holes not be much greater than the cross section area of the inside of the tubing. If the total area of the holes is much less than the area of the tube ID, you get strong jets of water from each hole. If the total area is much more than that of the tube ID, you get slower jets, and the holes farthest from the inlet to the tube may have very little flow out. When I was using this type of filter I didn't notice any stirring up of the mulm on the substrate. The flow from the jets gets diffused so much by the gravel that you can't see anything happening.

If there isn't much gravel over an area of the jets, you get a miniature gravel volcano, which doesn't look good. So, it seems that you have a choice of no visible effect or a bunch of miniature volcanoes.

You're more likely to have pressure differences from the front to the back of the line if you set the tubing in a spiral. A grid or manifold provides the same filtration effect using less tubing with even pressure across the system. 1/2" will work fine in this type of setup, with only one pump needed. I had a smaller pump running a similar system in a 20L. Wash the heck out of whatever substrate you use. I used turface and even with thorough washing the system blew out fine dust into the water as the substrate degraded from the constant flow of water.

Thank you for the replies,
I have gone over materials again, and am going to use 1/2" reduced to 3/8" tubing.
I will be using a spiral to avoid 90 degree bends (to prevent turbulent backpressure on the pump). Also two spirals will cover 90% of the bottom glass, and, with available materials, a grid pattern would only cover 72% of the bottom glass.

I am still struggling with size of holes, and how many. For testing I was going to use 12 1/16" holes on one closed loop spiral and see what happens. Depending on how the test goes, I may use the two opposing pumps idea.

Just tested the pump, it won't handle the back-pressure of only 3ft of 1/2" tubing, nevermind restricting the flow, just chatters like crazy.
Now searching for a pump that can handle the back-pressure of the system.

essabee;
Thank you very much for the link, Great idea/setup. Would work for me if I had a larger tank, and if I wanted to go the ugf route.
Based on the calculation you provided, I will need 200 square inches for the ugf, (based on the pump sitting here) my tank bottom is 288 square inches (12"x24").
Seeing as the gravel is 80% covered in plants/rocks/wood, I don't think this will work for my application.
Also I don't like pulling water through the gravel, due to my tank being overstocked, my biggest problem right now is constant gravel vacuuming. (as in every 3-5 days) I can see my intake pipes getting plugged quite often.
I am attempting to create an upwards current under the gravel on as close to 100% of the tank bottom as I can.
It is a great idea/setup, it's just not what I am attempting to do.
I'm trying to do more of a reverse ugf setup with a higher flow than just ugf plates with a reversed powerhead. (have to push through 4" of gravel on one end)

What kind of pumps did you use in your system? Do they "chatter" when backloaded?

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